1. Field of the Invention
The present invention relates to a spin-valve thin-film magnetic element including a free magnetic layer and laminates of pinned magnetic layers and antiferromagnetic layers formed on two surfaces of the free magnetic layer, and to a method for making the spin-valve thin-film magnetic element.
2. Description of the Related Art
Magnetoresistive magnetic heads are classified into anisotropic magnetoresistive (AMR) heads provided with elements having anisotropic magnetoresistive effects and giant magnetoresistive (GMR) heads provided with elements having giant magnetoresistive effects. An AMR head has a single layer structure of a magnetic element exhibiting a magnetoresistive effect. In contrast, a GMR head is provided with a multi-layered element composed of a plurality of layers exhibiting an anisotropic magnetoresistive effect. Several structures have been proposed to produce giant magnetoresistive effects. A spin-valve thin-film magnetic element has a simple structure and a high rate of change of resistance to a weak external magnetic field. Spin-valve thin-film magnetic elements are classified into single spin-valve thin-film magnetic elements and dual spin-valve thin-film magnetic elements.
FIGS. 12 and 13 are schematic cross-sectional views of a conventional spin-valve thin-film element.
Shielding layers are formed above and below the spin-valve thin-film element with gap layers therebetween, and a GMR head for reading is composed of the spin-valve thin-film element, the gap layers, and the shielding layers. An inductive head for recording may be deposited on the GMR head for reading.
The GMR head and the inductive head are provided at a trailing end of a floating slider and constitute a thin-film magnetic head. The GMR head detects recorded magnetic fields on magnetic recording media, such as hard disks. In FIGS. 12 and 13, a magnetic recording medium moves in the Z direction and a fringing magnetic field is generated in the Y direction from the recording magnetic medium.
The spin-valve thin-film magnetic element 3 shown in FIG. 12 is a so-called dual spin-valve thin-film magnetic element in which a nonmagnetic conductive layer, a pinned magnetic layer, and an antiferromagnetic layer are deposited on each of two surfaces of a free magnetic layer.
The dual spin-valve thin-film magnetic element includes two groups of triple-layer configurations, each including a free magnetic layer, a nonmagnetic conductive layer, and a pinned magnetic layer. Thus, this element has a large rate of change of resistance compared to a single spin-valve thin-film magnetic element having a single group of the triple-layer configuration including the free magnetic layer, the nonmagnetic conductive layer, and the pinned magnetic layer, and can be used in high-density recording.
In the spin-valve thin-film magnetic element 3 shown in FIGS. 12 and 13, an underlying layer 10, a second antiferromagnetic layer 11, a second pinned magnetic layer 12, a nonmagnetic conductive layer 13, a free magnetic layer 14 composed of Co films 15 and 17 and a NiFe alloy film 16, a nonmagnetic conductive layer 18, a first pinned magnetic layer 19, a first antiferromagnetic layer 20, and a protective layer 21 are deposited in that order from the bottom of the drawings.
As shown in FIG. 13, biasing layers 130 and conductive layers 131 are formed on two sides of the laminate over the underlying layer 10 to the protective layer 21.
The first and second pinned magnetic layers 19 and 12, respectively, are formed of, for example, a Co film, a NiFe alloy, a CoNiFe alloy, or a CoFe alloy.
The first and second antiferromagnetic layers 20 and 11, respectively, are formed of a PtMn alloy, an XMn alloy wherein X is at least one metal selected from Pd, Ir, Rh, Ru and Os, or a PtMnZ alloy wherein Z is at least one element selected from Pd, Ir, Rh, Ru, Os, Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr.
The first pinned magnetic layer 19 and the second pinned magnetic layer 12 in FIG. 12 are magnetized at interfaces with the first and second antiferromagnetic layers 20 and 11, respectively, by exchange anisotropic magnetic fields by exchange coupling (unidirectional exchange coupling magnetic fields), and the magnetization vectors are fixed in the Y direction in the drawing, that is, a direction (height direction) away from the recording medium.
The free magnetic layer 14 is aligned in a single-domain state by a magnetic flux from the biasing layers 130, and the magnetization is aligned in the X direction in the drawing, which is perpendicular to the magnetization vector of the first and second pinned magnetic layers 19 and 12, respectively.
Since the free magnetic layer 14 is aligned to a single-domain state by the biasing layers 130, the generation of Barkhausen noise is avoidable.
In the spin-valve thin-film magnetic element 3, when stationary currents flow from one conductive layer 131 to the free magnetic layer 14, the nonmagnetic conductive layers 18 and 13, respectively, and the first and second pinned magnetic layers 19 and 12, and when a fringing magnetic field is applied in the Y direction from the magnetic recording medium, which moves in the Z direction, the magnetization of the free magnetic layer 14 changes from the X direction to the Y direction. Such a change in magnetization vector in the free magnetic layer 14 causes a change in electrical resistance of the element in relation to the magnetization vector of the first and second pinned magnetic layers 19 and 12, respectively. The fringing magnetic field from the magnetic recording medium is detected as a change in voltage based on the change in electrical resistance.
In the production of this spin-valve thin-film magnetic element 3, individual layers from the underlying layer 10 to the protective layer 21 are deposited in that order, and are annealed in a magnetic field to generate exchange anisotropic fields at an interface between the first pinned magnetic layer 19 and the first antiferromagnetic layer 20 and at an interface between the second pinned magnetic layer 12 and the second antiferromagnetic layer 11 so that the first and second pinned magnetic layers 19 and 12, respectively, have the same magnetization vector (Y direction in the drawing).
In the conventional spin-valve thin-film magnetic element 3, as shown in FIG. 14, it is preferable that the magnetization vector (H3) of the free magnetic layer 14 be perpendicular to the magnetization vectors (H1 and H2) of the first and second pinned magnetic layers 19 and 12, respectively, when an external magnetic field is not applied from the recording medium. However, dipolar magnetic fields (H4 and H5) leaking from the first and second pinned magnetic layers 19 and 12, respectively, enter the free magnetic layer 14 from the opposite direction to the Y direction. These dipolar magnetic fields (H4 and H5) tilt the magnetization vector (H3) toward the vector (H6) opposite to the Y direction, and thus preclude biasing adjustment for orienting the magnetization vector of the free magnetic layer 14. As a result, the magnetization vector (H6) of the free magnetic layer 14 cannot be perpendicular to the magnetization vectors (H1 and H2) of the first and second pinned magnetic layers 19 and 12, respectively, and the regenerated waveform is inevitably asymmetric.